NEW MITICIDES VARY IN EFFICACY IN CONTROLLING TWOSPOTTED SPIDER MITES (Tetranychus urticae) IN ALFALFA HAY BASED ON GROWTH RESPONSE
Applied Research
Michael Rethwisch
Farm Advisor - Crop Production and Entomology
University of California Cooperative Extension
Blythe
Abstract
Twospotted spider mites (Tetranyhus urticae) have recently increased greatly in both population and damage to local alfalfa, with damage now occurring in at least 5 cuttings per year. Options for control are very limited with only one effective active ingredient (hexythiazox) available, with only one application/year of this active ingredient allowed. Reduced efficacy of this active ingredient is also being noted by pest control advisors and growers, thus a high need for additional products for effective control exists. Twelve treatments, including several potential new unregistered products, were applied on October 21, 2024, to alfalfa that was heavily infested with spider mites and was nearing cutting height using a back-pack sprayer delivering 20.2 gallons/acre of solution. Small plots (14 x 25 foot) with a randomized complete block experimental design were used, and included four replications of each treatment. Treated alfalfa was not cut to allow comparative miticide product evaluation on new growth under severe conditions, and would also be somewhat similar to long term feeding of spider mites in alfalfa seed production systems. Data were collected on December 2, 2024. Heights of five stems/plot were obtained in addition to percent of each plots that had green growth. These two factors were multiplied to obtain plant vigor for each plot, which was used to determine crop growth response to applied miticides. Data/treatment means were analyzed and separated using Tukey’s Honestly Significant Different test. Resulting information noted several treatments that resulted in a significantly higher plant vigor score than Hexamite® (which contains hexythiazox), with these being Kodama and both rates of Plinazolin (0.7 and 1.03 oz./acre). Two other products (Danitol® EC and Magister® SC) were very similar in plant vigor score to that of Hexamite®. While these products show promise as miticides in alfalfa hay, none are currently registered for usage on alfalfa hay or alfalfa seed. It is expected that the results from this field trial will be highly valuable in securing a future registration.
Poster has NOT been presented at any previous NACAA AM/PIC
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Authors: Michael Rethwisch
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Rethwisch, M. Farm Advisor - Crop Production and Entomology, University of California Cooperative Extension - Riverside County, California, 92225